I use pegboard for the bottoms of my nestbox. It drains for the first couple weeks. Sometime between 2-3 weeks I pull it, clean it out, and unscrew the pegboard, allowing the box to just sit on wire, but kits are plenty big enough by then.
Ditto on using good wire for the cage bottoms--14 ga gaw from klubertanz as well in mine. Huge difference between those I built and those I bought with 16 ga gbw mesh bottom. Worth the price difference to me.
Also--you may want to rethink the depth of cages. My 24" are tough enough to reach the back. Mine that I built--48" kindling cage in center, split top and bottom.
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